Genes make up about 2 percent of the human genome. The rest consists of a genetic material known as noncoding DNA, and scientists have spent years puzzling over why this material exists in such voluminous quantities.

A team of researchers, led by University of Kentucky ophthalmologist Dr. Jayakrishna Ambati, has discovered a molecular mechanism implicated in geographic atrophy, the major cause of untreatable blindness in the industrialized ...

Researchers from the University of Leeds, UK, the Charite University Medical School and the Max Delbruck Centre for Molecular Medicine (MDC) in Berlin, Germany, have discovered a new driving force behind cancer growth.

The Y chromosome, that little chain of genes that determines the sex of humans, is not as tough as you might think. In fact, if we look at the Y chromosome over the course of our evolution we've seen it shrink at an alarming ...

(Phys.org) —Transposons are DNA elements that can multiply and change their location within an organism's genome. Discovered in the 1940s, for years they were thought to be unimportant and were called "junk DNA." Also ...

What allows certain plants to survive freezing and thrive in the Canadian climate, while others are sensitive to the slightest drop in temperature? Those that flourish activate specific genes at just the right time—but ...

MIT biologists have discovered a mechanism that allows cells to read their own DNA in the correct direction and prevents them from copying most of the so-called "junk DNA" that makes up long stretches of our genome.

Junk DNA

In evolutionary biology and molecular biology, junk DNA is a provisional label for the portions of the DNA sequence of a chromosome or a genome for which no function has been identified. The term was introduced in 1972 by Susumu Ohno, but is as of 2008 somewhat outdated, being used mainly in popular science and in a colloquial way in scientific publications. For some sequences once classified as junk DNA, functions have been found, and others are subject to ongoing research. About 95% of the human genome has once been designated as "junk", including most sequences within introns and most intergenic DNA. While much of this sequence may be an evolutionary artifact that serves no present-day purpose, some junk DNA may function in ways that are not currently understood. Moreover, the conservation of some junk DNA over many millions of years of evolution may imply an essential function. Some consider the "junk" label as something of a misnomer, but others consider it appropriate as junk is stored away for possible new uses, rather than thrown out; others prefer the term "noncoding DNA" (although junk DNA often includes transposons that encode proteins with no clear value to their host genome). About 80% of the bases in the human genome may be transcribed, but transcription does not necessarily imply function.

Broadly, the science of functional genomics has developed widely accepted techniques to characterize protein-coding genes, RNA genes, and regulatory regions. In the genomes of most plants and animals, however, these together constitute only a small percentage of genomic DNA (less than 2% in the case of humans). The function, if any, of the remainder remains under investigation. Most of it can be identified as repetitive elements that have no known biological function for their host (although they are useful to geneticists for analyzing lineage and phylogeny). Still, a large amount of sequence in these genomes falls under no existing classification other than "junk". For example, recent experiments removed 1% of the mouse genome and were unable to detect any effect on the phenotype. This result suggests that the DNA is nonfunctional. However, it remains a possibility that there is some function that the experiments performed on the mice were merely insufficient to detect. This can also be evidence for reconstructing ancestral lineages.

While overall genome size, and by extension the amount of junk DNA, are correlated to organism complexity, there are many exceptions. For example, the genome of the unicellular Amoeba dubia has been reported to contain more than 200 times the amount of DNA in humans".

The pufferfish Takifugu rubripes genome is only about one tenth the size of the human genome, yet seems to have a comparable number of genes. Most of the difference appears to lie in what is now known only as junk DNA. This puzzle is known as the C-value enigma or, more conventionally, the C-value paradox.